diff --git a/libavcodec/dtsdec.c b/libavcodec/dtsdec.c
index 128d60f9ba..fb1d50c10e 100644
--- a/libavcodec/dtsdec.c
+++ b/libavcodec/dtsdec.c
@@ -208,8 +208,6 @@ dts_decode_frame (AVCodecContext *avctx, void *data, int *data_size,
 {
   uint8_t * start = buff;
   uint8_t * end = buff + buff_size;
-  *data_size = 0;
-
   static uint8_t buf[BUFFER_SIZE];
   static uint8_t * bufptr = buf;
   static uint8_t * bufpos = buf + HEADER_SIZE;
@@ -221,6 +219,8 @@ dts_decode_frame (AVCodecContext *avctx, void *data, int *data_size,
   int len;
   dts_state_t *state = avctx->priv_data;
 
+  *data_size = 0;
+
   while (1)
     {
       len = end - start;